The long-term objective of this proposed research is to develop a simple, inexpensive point-of-care device that will perform absolute and percent CD4+ T cell counts from whole blood. This will be accomplished by adapting and testing a novel "hybrid" approach to microfluidic sample preparation and analysis. One-time use thin-film laminated microfluidic cassettes will collect, count, and store the blood sample while the required cocktail reagents will be stored and injected into the cassettes from a bench-top unit. The integrated system will perform a total white blood cell count, absolute CD4+ T cell count, and percent CD4 count using a new volumetric combination electric impedance/fluorescence sensor contained on a disposable microfluidic cassette. Toward this objective, Phase II will expand on our Phase I effort and focus on system optimization and validation. Aim one will optimize the microfluidic cassette design and CD4 blood labeling protocol for automated, on-card CD4+ T cell counting. Aim two will focus on fabrication and testing of the integrated bench-top system. Aim three will test and validate the completed CD4 enumeration system, using both modified commercially available normal human whole blood and clinical samples from HIV+ patients, and begin the bench-top studies required to obtain FDA clearance for a Class II medical device. The resulting device, when fully validated and evaluated in the proposed scenarios of use, will be simple, robust, and unique in that it provides a fully quantitative CD4+ T cell analysis with an instrument costing less than $1000. This is many times below the cost of established flow cytometry devices. Reagent and disposable costs will also be lower than that of any currently available device with per-test total costs of less than $1.50. The tool will find immediate application in all levels of the public health care system, particularly in resource-poor areas and developing countries, for monitoring persons with human immunodeficiency virus (HIV), formulating differential diagnoses, and making therapeutic decisions regarding anti-retroviral drug treatment regimes, including the highly active anti-retroviral therapy (HAART) approach. PUBLIC HEALTH RELEVANCE The successful completion of an inexpensive, portable CD4 counter would constitute a significant breakthrough in HIV monitoring and treatment by offering healthcare providers a less expensive, mobile platform to conduct the most common CD4 diagnostic test currently performed in the world. Such a breakthrough will dramatically improve testing efficiencies with its single-use, disposable test cartridges and will make it possible to rapidly test patients at bedside, in remote locations, or in areas with limited healthcare resources. Finally, this new point-of-care system could significantly reduce current CD4 equipment and per-test costs, thereby resulting in millions of dollars saved in the US healthcare and insurance industries, with even greater worldwide healthcare impacts in developing countries.